a) Technological Field
This invention relates to an online internal qualities inspection system for non-destructively inspecting and measuring the internal qualities such as sugar forming degree, acidity, etc. of the objects of inspection, such as agricultural products, by projecting beams of light on each of the objects from on both the right and left sides thereof and by receiving and spectrally analyzing the light transmitted through the objects of inspection while they are in the process of being conveyed on receiving trays or the like by various transport means.
b) Background Art
The types of known methods for measuring the internal qualities of agricultural products include a reflection light type method and a transmission light type method. In the case of the former type, information on the internal qualities is detected through a reflection light obtained from the agricultural product by projecting on the agricultural product beams of light including near infrared rays. In the latter, information on the internal qualities is detected from the transmittance through the agricultural product of the light projected on the agricultural product.
According to the reflection light type method disclosed, for example, in Japanese Laid-Open Patent Application No. HEI 6-300681, the method is carried out by projecting beams of light including near infrared rays onto a measuring (inspecting) object and by detecting the information on the internal qualities of the object from the light reflected by the object as a result of light projection thereon. In carrying out the method, a conventional screening (sorting) device having receiving trays arranged to convey agricultural products one by one is used as it is. However, the internal qualities information obtainable by this method is limited to information on a peripheral part and a part near to it of the agricultural product where the projected light is received. Although this method is applied to a fruit having a thin skin, such as peaches and pears, the internal qualities information obtained by this method fluctuates according to the parts of even one and the same agricultural product. It gives a good result of inspection for a part which has been on a sunny side and a bad result for a part which has been on a shadowy side. It is also incapable of detecting such a honey forming part located deep inside and near to the core of a fruit. Besides, in the event of a fruit having a thick skin, the method gives information only on the thick skin part and not on the edible, flesh part of the fruit.
A system using the transmission light type method was disclosed in Japanese Laid-Open Patent Application No. HEI 7-229840. In this system, a single unit of light projecting lamp is arranged as a light source on one side of the transport path of a transport belt conveyer. A light receiving part is arranged opposite to the light projecting lamp to have an optical axis straightly across the transport path. The system is thus arranged to project light on one side of an agricultural product being conveyed for inspection and to detect light transmitted sidewise through the agricultural product from the other side thereof. However, since the system has only one light projecting lamp, the light projected is limited in intensity and quantity. In the event of an agricultural product having a thick skin or a low water content in its flesh part, therefore, the transmitted light is too weak for spectral analysis. In such a case, therefore, errors in the results of spectral analysis tended to increase to degrade the accuracy of measurement made by the system of this type in the past.
Further, the measured value obtained by the above-stated system by projecting light from one light projecting lamp fluctuates greatly according to the direction in which the light is projected by the lamp to lower the accuracy and reliability of measurement. Another shortcoming of the system lies in that, since the light receiving part is arranged to have a diffraction grating directly connected thereto, the size of a case required for housing the light receiving part therein becomes too large.
The above-stated system is arranged lo shut off the rays of light of the light projecting lamp by means of a shutter solenoid when the light projection is not required in the case of a suspension of operation or the like. However, while rays of projection light is shut off, variations of disturbance light such as ambient light or the like tend to come through a condenser lens into the light receiving part to cause fluctuations in the zero level (dark current) of a light receiving element.
Further, in order to cause light to penetrate a thick-skinned agricultural product, such as oranges, melons, watermelons or the like, with a single light projecting lamp used, the lamp must be arranged to have a high degree of output. However, the use of a high-output lamp necessitates some lamp cooling arrangement as the lamp generates high temperature heat. Besides, since the light is converged onto the agricultural product by means of a reflection mirror, the light converging part is heated to such a high temperature that exceeds 500 degrees. The high temperature has necessitated use of a heat resisting material and presented the hazard of fire. Further, the filament of the high-output lamp is large. The large filament of the lamp not only makes the light converging arrangement difficult but also has a short service life. The lamp thus cannot be used over a long period of time, because its illuminating power gradually decreases.
In view of these problems, the applicant of the present application has developed and practicalized internal qualities inspecting devices of the transmission light type which are capable of detecting information on the internal qualities of citrus fruits or oranges, melons, watermelons, etc. having thick skin parts and the honey forming parts or brown scarred parts existing deep inside of apples or the like. These devices are disclosed in Japanese Laid-Open Patent Applications No. HEI 6-288903 and No. HEI 10-202205. Each of these devices is arranged to use transport means having agricultural product receiving trays. Each of the receiving trays is provided with a receiving seat which is arranged to shield, from disturbance light, a weak light transmitted through the inside of the agricultural product under inspection. The receiving seat is provided with a transmission light passage which vertically penetrates the receiving seat. The light receiving part of the device is arranged to be opposed to the lower center part of each of the receiving trays when they are traveling. Since the transport means is using the receiving trays which are thus arranged for the internal qualities inspecting device, the device can efficiently detect the transmitted light. However, if the device is arranged to be capable of sufficiently obtaining the transmission light from the object of inspection even in the case where the object is of such a kind that does not readily transmit the light, the operational amplifier of a spectral analyzer would come to overflow to make internal qualities analysis impossible.
Further, in order to assure an online internal qualities inspection device stably operates over a long period of time, the device must be constantly calibrated, because of variations taking place in environment temperature in the morning, daytime and evening and variations taking place during the lapse of operation time. However, conventional online internal qualities inspection devices are provided with no mechanism necessary for stably calibrating them.
In addition to this problem, the variations in environment temperature and the lapse of the operation time have caused deviations of a calibration curve.